1. Field of the Invention
The present invention relates to a semiconductor device and a manufacturing method thereof and more particularly to a semiconductor device at high integration degree and of high speed operation, and a manufacturing method thereof.
2. Description of the Related Art
In recent years, with a view point of increasing the integration degree and the operation speed of semiconductor devices, decrease in the inter-wiring capacitance has been required. Then, studies have been made vigorously for introducing dielectric films of lower dielectric constant than existent silicon oxide films (dielectric constant: 3.9-4.2) as inter-wiring dielectric films (hereinafter simply referred to as low dielectric constant films).
Typical low dielectric constant films of dielectric constant of 3 or less can include, for example, organic siloxane films, inorganic siloxane films and aromatic organic polymer films. The organic siloxane films contain at least methyl groups (—CH3). Methyl siloxane (MSQ) film and methylate hydrosiloxane (HMSQ) film are typical and methylate hydrosiloxane (HMSQ) film are typical examples. Further, inorganic siloxane films contain no methyl groups and hydrosiloxane (HSQ) films are typical examples.
Porous low dielectric constant films of further lower dielectric constant (dielectric constant; 2.5 or less) have also been studied and, particularly, porous organic siloxane films have often been studied because they are excellent, for example, in moisture resistance, chemical resistance, and mechanical strength.
However, the organic siloxane film involves a problem that adhesivity with a dielectric film at the upper layer is extremely low, which hinders practical application. Problems present in forming existent damascene copper wirings are to be described for the example of an organic siloxane film as an inter-level dielectric film (FIG. 1A to FIG. 2C).
At first, as shown in FIG. 1A, after forming a second inter-level dielectric film 7 on a substrate 21 including semiconductor devices and wirings, an organic siloxane film 8 is formed. The organic siloxane film 8 is generally formed by a spin-on coating method or a CVD (chemical vapor deposition) method. A silicon carbide film, a silicon oxide film or a silicon nitride film is formed to about several tens nanometers as a dielectric protection film 10 on the organic siloxane film 8. The dielectric protection film is formed with an aim of preventing the organic siloxane film 8 from degradation in the subsequent resist removing step by plasma ashing or polishing step for metal films. Successively, after forming a resist mask (not illustrated) on the dielectric protection film 9, first layer wiring trenches 11 are formed by dry etching as shown in FIG. 1B, and the resist mask is removed by plasma ashing. As shown in FIG. 1C, a titanium nitride film or a tantalum nitride film is formed thinly as a barrier metal film 12 and, further, a copper film 13 is formed. Finally, as shown in FIG. 2A, metals other than those in the first layer wiring trenches 11 are removed by a CMP (Chemical Mechanical Polishing) method to form conduction portions such as wirings or inter-level connection.
In the semiconductor device obtained by the procedures described above, since the organic siloxane film 8 of low dielectric constant is used as the inter-wiring dielectric film, the capacitance between wirings can be decreased effectively. However, adhesivity between the organic siloxane film 8 and the dielectric protection film 10 formed thereon is generally poor and delamination tends to occur during a CMP step or the like as shown at a delamination portion 22 in FIG. 2B. Such delamination results in deterioration of the reliability of wirings and lowering of the yield in the wiring steps.
For preventing the delamination failure, it has been studied a method of applying a plasma treatment just after the deposition of the organic siloxane film 8 to form an existent modified layer 23 on the surface thereby improving the adhesivity as shown in FIG. 2C. The modified layer is a layer formed by the plasma treatment on the surface of the organic siloxane film and having a carbon content lower than that of the organic siloxane film. For forming the existent modified layer 23, an oxygen gas has been used most generally as a plasma gas and water, ammonia, nitrogen, argon, hydrogen, helium or neon gas has also been known as other gas.
A method of improving the adhesivity by the plasma treatment using an active gas such as an oxygen gas or a gas mixture of ammonia and nitrogen has been disclosed in “Integration of Low k Methyl Silsesquioxane in a Non-Etchback/CMP Process for 0.25 μm LSI Device” H. D. Joeng, et al., Proceedings of International Interconnect Technology Conference, 1999, pp. 190-192). At the surface of the modified layer formed by the plasma treatment using the active gas described above, the carbon content is decreased to about ⅕ of the carbon content in the organic siloxane film. As described above, since carbon causing that lowers the adhesion strength is decreased, film delamination can be prevented. However, since carbon is greatly decreased in the modified layer, the modified layer has high hygroscopicity. As a result, this results in a problem of increasing the dielectric constant and also increasing the effective capacitance between wirings. It is considered that a similar problem will occur even when water is used as an active gas.
As another example, a method of applying a plasma treatment to the surface of a non-siloxane type organic dielectric film by using an inert gas such as nitrogen, argon, hydrogen, helium or neon, there by improving the adhesivity to the dielectric film on the upper layer has been disclosed JP-A No. 106364/2000. Also in a case of applying the plasma treatment to the organic siloxane film using the inert gas, since the carbon content in the modified layer is decreased greatly, increase of the dielectric constant is inevitable.
Further, a further example of applying the plasma treatment on the surface of the organic siloxane film can include an etchback process. The etchback process is a process of forming a coated type organic siloxane film so as to fill a gap between metal wirings having unevenness and then conducting planarization by etching the organic siloxane film using a fluorocarbon type gas. Such a process is not effective for the improvement of the adhesivity. This is because the fluorocarbon type polymer deposits on the organic siloxane film to rather lower the adhesion strength. In the etchback process, an oxygen gas or an argon gas is usually irradiated for removing the gas fluorocarbon polymer, but the dielectric constant of the organic siloxane film is increased in this case.
A method of lowering the dielectric constant of the organic siloxane film increased by the plasma treatment is disclosed in JP-A No. 58536/2000. In this example, in the resist removing step using oxygen plasmas, the dielectric constant of the organic siloxane film exposed to the sidewall of the hole is increased. Then, the increased dielectric constant is lowered by a plasma treatment using one of a gas mixture of hydrogen and nitrogen, a fluorine gas, or a hexamethyl silazane gas. In this method, since a high reactive oxygen is irradiated to the organic siloxane film, the dielectric constant is increased greatly. Therefore, even if the dielectric constant is lowered by the plasma treatment of using the gas described above, the dielectric constant cannot be recovered to the same value as in the original organic siloxane film.